The class of foams known as low density rigid polyurethane or polyisocyanurate foam has utility in a wide variety of insulation applications including roofing systems, building panels, refrigerators and freezers. A critical factor in the large-scale commercial acceptance of rigid polyurethane foams in the building insulation industry has been their ability to provide a good balance of properties. Rigid polyurethane and polyisocyanurate foams are known to provide outstanding thermal insulation, excellent fire properties and superior structural properties at reasonably low densities.
The methods of producing polyurethane and polyisocyanurate foams are known and consist in general of the reaction of an organic polyisocyanurate (including diisocyanate) and a polyol or mixture of polyols in the presence of a volatile blowing agent, which is caused to vaporize by the heat liberated during the reaction of isocyanate and polyol. This reaction can be enhanced through the use of amine and/or other catalysts as well as surfactants. The catalysts ensure adequate curing of the foam, while the surfactants regulate and control cell size. Flame-retardants are traditionally added to rigid polyurethane or polyisocyanurate foam to reduce its flammability.
The foam industry has historically used liquid fluorocarbon blowing agents such as trichlorofluoromethane (CFC-11) and 1,1-dichloro-1-fluoroethane (HCFC-141b) because of ease of use in processing conditions. Fluorocarbons act not only as blowing agents by virtue of their volatility, but also are encapsulated or entrained in the closed cell structure of the rigid foam and are the major contributor to the low thermal conductivity properties of rigid urethane foams.
The use of a fluorocarbon as the preferred commercial expansion or blowing agent in insulating foam applications is based in part on the resulting k-factor associated with the foam produced. K-factor is defined as the rate of transfer of heat energy by conduction through one square foot of one inch thick homogenous material in one hour where there is a difference of one degree Fahrenheit perpendicularly across the two surfaces of the material. Since the utility of closed-cell polyurethane-type foams is based, in part, upon their thermal insulation properties, it would be advantageous to identify materials that produce lower k-factor foams than those above.
Many such blowing agents currently used for thermoset foams (PUR/PIR/Phenolic) also suffer from environmental or performance disadvantages. Concern has increased in recent years about potential damage to the earth's atmosphere and climate, and certain chlorine-based compounds have been identified as particularly problematic in this regard. The use of chlorine-containing compositions (such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and the like) has become generally disfavored because of the ozone-depleting properties associated with many of such compounds. There has thus been an increasing need for new fluorocarbon and hydrofluorocarbon compounds and blends of existing compositions that offer alternatives for foaming applications. Blowing agents with above atmospheric boiling points characteristically have poor low temperature thermal performance. Thus, ideal blowing agents or agent blends should be a LGWP material that has optimal performance over a wide temperature range.
Hydrohaloolefins like 1,1,1,4,4,4-hexafluorobutene (1336mzzm) and 1-chloro-3,3,3-trifluoropropene (1233zd) are being independently developed as stand alone agents to meet these requirements. One problem associated with 1336mzzm, however, is that it has an elevated boiling point and contains 6 fluorine atoms in its structure. Thus, by itself, it exhibits several of the foregoing disadvantages, which makes it less valuable and cost prohibitive as an agent.
Accordingly, blowing agents are desirable in the art that exhibit low k-factor values, low global warming potential, low molecular weight, cost effective and optimal performance over a wide temperature range. The present invention addresses each of the foregoing in the embodiments and examples provided herein.